The function call `calculate_root_inline` calculates the merkle root
using the input array as a scratch buffer, i.e., we trash the data
during recursive calls to `merkle_root_r`.
Add explicit documentation to the function so its super clear not to use
the hashes again after calling this function.
Recently we renamed the `hash` module to `merkle_root`, this makes the
public functions provided stutter if used with one layer of path as is
Rust convention:
`merkle_root::bitcoin_merkle_root`
We can improve on this by renaming the functions to 'calculate', then we
get
- `merkle_root::calculate()`
- `merkle_root::calculate_inline()`
The `util::hash` module provides two functions for computing a merkle
root from a list/iterator of hashes.
Rename the module to `merkle_root` and move it to the crate root,
deprecate the original functions.
Done as part of flattening the `util` module.